FIG. 1 is a perspective view of a conventional carriage assembly as described in Japanese patent application No. 57-93897.
The carriage assembly shown in FIG. 1 includes a carriage 11 on which a pickup 12 is mounted; outer case yokes 13 of magnetic circuits constituting fixed-side driving sources; permanent magnets 14 fixed to, for instance, the outer case yokes 13; center pole pieces 15 of the fixed-side driving sources installed on both sides of the carriage 11 for driving the carriage 11, the fixed-side driving sources including the outer case yokes 13, the permanent magnets 14, and the center pole pieces 15; movable side coil bobbins 16 on which driving coils 17 are wound, the movable elements including the carriage 11, the pickup 12, coil bobbins 16, and the coils 17; bearings l8a and l8b for supporting the movable elements; and guide rails l9a and l9b.
The operation of this carriage assembly is as follows:
The outer case yokes 13 on both sides of the carriage 11, the permanent magnets 14, and the center pole pieces 15 constitute magnetic circuits, the direction of the magnetic field produced thereby pointing in the directions Y and Z indicated in FIG. 2. The coil 17 passes across the magnetic field formed by the magnetic circuit, whereas the current flows in the direction Z against the direction Y of the magnetic field and in the direction Y against the direction Z of the magnetic field. Consequently, the driving force acts in the direction X indicated in FIG. 2. When a target position on a disk has been determined, current is made to flow through the coils 17 in response to instructions from a control unit (not shown), and the carriage 11 is controlled by the driving force so as to move to the target position.
Subsequently, the carriage supporting structure will be described.
Two pairs of bearings l8a, namely, two bearings in front and in rear, are attached to the bottom of the carriage 11, extending generally in the direction of carriage movement with axis of the bearing l8a lying at a certain angle to the XY plane in FIG. 2 and the pair of left- and right-hand bearings l8a being respectively inclined in directions opposite to each other. As the bearings l8a are pressed against the guide rail l9a, they restrain the rotational moments of the carriage 11 around the Y and Z axes and its transverse and downward movement. Moreover, the bearings l8b, attached to both sides of the carriage 11 and pressed against the guide rails l9b installed on both sides of the carriage 11, restrain rotational movement of the carriage 11 around the X axis and upward movement of the carriage 11. Consequently, the movable elements make smooth linear reciprocal movements in only the longitudinal direction (the X direction).
In the conventional carriage assembly thus constructed, as three guide rails l9a, l9b and l9b and two pairs of fixed-side driving sources are required to reciprocate the carriage 11 linearly and smoothly, the width of the assembly is relatively great, as seen in FIG. 3. Also, there are problems such as high production costs because both the number of parts and the number of assembly steps are high. Moreover, the guide rails l9a installed on the bottom of the carriage 11 and the coils 17 on both sides thereof make the total height and width of the overall assembly great.